Hawaii Shelf Collapse 12-2005

The following set of slides is of a recent shelf collapse on the Big Island of Hawaii. During the 2005 Advanced Geology trip to Hawaii, we hiked out to a viewpoint that was close to where this collapse took place. The day we hiked out there, there was a minor collapse that essentially led to this major one. We of course hiked well inland of the coast.

Current lava pictures were taken from http://hvo.wr.usgs.gov/kilauea/update/#video slides 3,4, 19, 22, 27, 32, 33, 34 taken by Dan Brownstein

The images are all from June 29th to Dec 3rd 2005

Slide Show by Daniel Brownstein

We were standing several hundred feet upslope of the circle (see next slide). Note that there are several breakouts just beyond that. This picture is from June 30 th and we were there on the 29th. Check out the fractures (red and blue ovals) that were right below us in the delta. This is where the collapse took place. Everything to the left of that fracture (the red one) is in the ocean now. The new cliff is 100 ft!

What we saw from that vantage point

The steam plume on June 29th—visible from over 40 miles away

We were right here on June 29th!

Our approximate path

Approx ¼ mile

July 7 2005

Close up of lava delta July 2005. Note huge crack formed the previous day.To the left of the crack is “spatter” that came out of the crack when it formed. Lava is visible entering the ocean at the bottom left

Why Shelves Collapse

• Lava pours into ocean chaotically

• Layer upon uneven layer leads to a small delta

• Undercutting by ocean destabilizes delta

• Eventually the delta will collapse

• This sometimes forms a series of “steps”

• A drop down ledge is called a “bench”

• Next slide diagrams this process

1

4

3

2

November 1st

December 1st

X We were here

November 1st

December 1st45 acres of landfell into the ocean

Before (above)After (below)

Point A

Point A

Point B

Point B

Where you shouldn’t stand

Pictures of current flow into ocean over new cliff

Note that after 2 days—small delta/cone has built up below lava falls

1. Note location of lava tube (now exposed in cliff face)

2. Note gypsum/sulfur deposits that formed along new crack near cliff face—these commonly form along fractures above underground lava (see next slide)

Dec 22005

Pu’u O’o—current site of eruption—along Kilauea’s East Rift Zone

From here—lava travels mainly underground to ocean via lava tubes

Lava tubes form because the surface of a lava flow will cool first. Basalt is an excellent insulator and keeps lava underneath new crust relatively hot, which allows it to flow rapidly. When lava cools, it becomes thicker (more viscous) and slows down.

Lava tube cave—when lava stops flowing it can leave behind a cave like this one. This lava tube is

part of a miles long set of tubes on Mauna Loa

Current pahoehoe flows. Note that within the flow there are black specks. These are solidified pieces of basalt, which slows down the lava

Pahoehoe

When solidified, pahoehoe looks like this:

Skylight into Lava Tube: Since the top portion of the tube is relatively thin, pieces of the tube can collapse, forming a “skylight.”

Skylight into Lava Tube—October 2005

Psychotic Geologists

The geologic history of Hawaii is filled with examples of much more

catastrophic island collapses

These collapses can create “mega tsunamis” with waves over 2000 feet tall. Shells carried from such waves have been found thousands of feet above sea level on some of the Hawaiian volcanoes.

The Na’ Pali Coast (3500ft)—Kauai

The Kohala Coast—Big Island

Kalaupapa Pali (4000ft)—Molokai